We present Cider, an operating system compatibility architecture that can run applications built for different mobile ecosystems, iOS or Android, together on the same smartphone or tablet. Cider enhances the domestic operating system, Android, of a device with kernel-managed, per-thread personas to mimic the application binary interface of a foreign operating system, iOS, enabling it to run unmodified foreign binaries. This is accomplished using a novel combination of binary compatibility techniques including two new mechanisms: compile-time code adaptation, and diplomatic functions. Compile-time code adaptation enables existing unmodified foreign source code to be reused in the domestic kernel, reducing implementation effort required to support multiple binary interfaces for executing domestic and foreign applications. Diplomatic functions leverage per-thread personas, and allow foreign applications to use domestic libraries to access proprietary software and hardware interfaces. We have built a Cider prototype, and demonstrate that it imposes modest performance overhead and runs unmodified iOS and Android applications together on a Google Nexus tablet running the latest version of Android.

It's developed by the Department of Computer Science at Columbia University. They have a video of it too.

That's the first thing that sprang to my mind too. Especially as the projects are very similar: a software compatibility layer to run apps from platform $FOO on the Apple platform. The only difference is the value of $FOO. That's close enough to actually confuse users (as opposed to 99% of trademark disputes out there).

Cider is obviously a clever name for this, but others had already thought of it before...
The big question for me, what have I been missing? For which iOS application should I be forking out a fair sum??